1. Field of the Invention
The present invention relates to a method and apparatus for determining the condition of an image capture system. More particularly, the present invention relates to a method, apparatus and computer program product for determining the quality of performance of an image capture system while it is capturing images which are being scanned using imaging apparatus, such as a document scanner.
2. Description of Related Art
Banks routinely process checks and other financial instruments based on information gleaned from a digital image of a document. These checks are processed at high speed and any attempt to monitor the condition of the image capture and analysis system by visually inspecting sample images or inserting sample test paper documents into the document path seriously impacts the throughput of the system. Accordingly, there has been a need for a method and apparatus that continuously checks the health of an image capture system without human intervention while the system is in operation.
As users of image processing place more and more reliance on the captured images, the need to ensure that the image capture system is reliably capturing high quality images becomes acute. Reliability is ensured in the known art by scheduling preventative maintenance on a conservative more often than actually required basis. Examples of methods for scheduling maintenance on a time and/or usage basis is described in IBM Technical Disclosure Bulletin, February 1994, pages 645 through 647, and IBM Technical Disclosure Bulletin May 1998, page 5338.
Such continued maintenance keeps the system running smoothly but is costly both from service costs and system down time points of view. Even when maintained on a very frequent schedule, there often occurs a situation where excessively dirty or dusty documents or other unusual conditions cause the performance of an image capture system to deteriorate beyond acceptable limits and the system shuts down with an error condition. Even worse, the system may not shut down but continue to capture inferior images until the reduced quality is noted manually by an operator or user of the images. By that time it may be too late to easily recover acceptable images as the originals may have been sent away or even destroyed. Such reduced quality may originate in systems where video gain and offset is automatically increased to compensate for illumination degradation, paper dust and other irregularities.
A typical technique for determining the present level of scanner and system performance or deterioration is to present a test target to the scanner and analyze the scanner output. The problem is that this interferes with normal use of the scanner and reduces scanner throughput. In one example of slower speed document scanning, a test target comprises a white area in the object plane of the scanner. The white area is scanned between original documents being scanned. In this example, the extra scans are feasible because in lower speed operation with adequate spacing between documents being scanned, there is time available between documents being transported through the scanner for these extra scans. In higher document speed scanners, throughput is critical and documents are spaced as close together as possible so that time is not available for the extra scan cycles. Furthermore the white area in the object plane can itself become degraded. Such degradation will then give a false indication of system condition. The system itself may still be operating within acceptable tolerances but the measuring reference white area may have become dirty. Also as described above, automatic gain control based upon a reference area may mask the negative effects of dust and illumination control but the increased gain degrades the signal to noise ratio.
Some known techniques such as histogram analysis attempt to determine the health or condition of an image capture and processing system without extra scan cycles. Histogram analysis examines scanner output to determine if one gray level is more prevalent in the image than any other gray level. Such histogram techniques make assumptions about the type of document that will be scanned. For example, multi-shade or color documents must be analyzed differently from other documents. Therefore histogram techniques are only useful for certain applications such as in diagnostic mode testing. These techniques are also insensitive to isolated picture element failures.
U.S. Pat. No. 5,149,977 of Mita describes a document reader apparatus that automatically detects document skew and inappropriate contrast due to the document itself or to inappropriate binary thresholding. Multiple sensors 116-1 to 116-4 are used to determine whether any part of the document has been lost due to skew.